The present invention relates generally to detection of the onset of a rapid drop in a patient's blood pressure in connection with extracorporeal blood treatments, such as hemodialysis (HD), hemofiltration (HF) or hemodiafiltration (HDF).
The human body consists of approximately 60% water—a level which is important to maintain for survival. While it is unproblematic to provide the body with new water, disposal of surplus water is a major problem in renal patients. The task of the normal kidney is to remove superfluous fluid from the blood, such as water, urea and other waste products. The resulting urine is transferred to the bladder and finally leaves the body during urination. The kidney's second task is to regulate for example the balance of acid and base. With malfunctioning kidneys, disorders may develop in most major body organs, a syndrome called uremia. If uremia remains untreated, it will lead to death. Uremia is treated either by kidney transplantation, or some form of blood treatment, extracorporeal or intracorporeal
Due to extensive fluid extraction during extracorporeal blood treatment, it is common that the patient suffers from symptomatic hypotension, characterized by a blood pressure drop and symptoms such as cramps, nausea, vomiting and sometimes fainting. Such an event is not only strenuous for the patient, but also requires considerable attention from the staff overseeing the treatment. Consequently, when performing extracorporeal blood treatment, it is highly desirable to detect the onset of symptomatic hypotension and preventing it from coming about. Moreover, before initiating the treatment of a given patient, it is important to estimate whether or not this patient is especially inclined to encounter hypotension related problems, i.e. is hypotension-prone, so that the treatment parameters can be adapted appropriately.
In the article, “Can Haemodialysis-Induced Hypotension be Predicted?”, Nephron 2002; 92:582-588, Cai, Y. et al. conclude that in HD patients hypotension is brought out by a reduction in the central blood volume. Namely, such a volume reduction, in turn, affects the heart rate and the distribution of red cells within the body unfavorably. The article suggests that HD-induced hypotension be prevented by reducing the ultrafiltration rate when an increase in the thoracic impedance approaches 5Ω, or when an admittance index of intracellular water decreases by 6·10−4.
The published international patent application WO 2005/094498 discloses a solution for monitoring thoracic impedance by means of an electrode array. Here, it is stated that for instance renal disease correlates with the level and variation of the level of intrathoracic fluids. Nevertheless, no strategy is proposed by means of which this information is used to predict hypotension.
Hence, although relationships between the onset of hypotension and variations in the central blood volume/thoracic impedance have been discovered, no solution exists, which is capable of utilizing these relationships to identify dialysis patients being especially prone to suffer from symptomatic hypotension.